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San Andreas Fault

San Andreas Fault. Introduction. We live next to this fault It’s active It has a history of major earthquakes We had better know something about it ..so that we can better prepare. Features-1. Not recognized (in total) until ~1940

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San Andreas Fault

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  1. San Andreas Fault

  2. Introduction • We live next to this fault • It’s active • It has a history of major earthquakes • We had better know something about it • ..so that we can better prepare

  3. Features-1 • Not recognized (in total) until ~1940 • Not recognized as a plate boundary until ~1970 – plate tectonic theory had to happen first! • Named after Lake San Andreas (SW of San Fransico) following the 1906 earthquake

  4. Features-2 • Plate boundary between N. American and Pacific plates • Motion is transform with the Pacific plate moving northward

  5. Plate features

  6. Features-3 • Active since 23.5 my BP; total = 315 km • Long-term rate = 1.3 cm/year • NOTE – there have been other strands and similar faults have occurred in the region since ~~60 my BP; ~~480 km offset of Baja California peninsula

  7. Major California Earthquakes

  8. Complexity in detail

  9. Note that foundations matter

  10. Response of different Earth foundations

  11. Pallett Creek Work of T. Sieh, ~1987 Ph.D., California Tech.

  12. Pallett Creek

  13. Detailed map of sag-pond sediments across fault

  14. Key to understanding • C-14 dating of organic material • Carefully relating ages to offset of pond sediments

  15. Summation of findings • Covers 1700 years • Median frequency = one per 132 years • Range 50 – 500 years

  16. Ft. Tejon earthquake

  17. Features • 1857 (before reliable, common seismometers and reproducible results) • Magnitude ~8.0 • Offset near epicenter ~ 9 m

  18. Ft. Tejon

  19. Rupture • and felt area

  20. Note that this break extended to Pallett Creek

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